1. Field of the Invention:
This invention relates to concrete screeding apparatus and particularly to portable vibrating screeds for screeding relatively narrow wet concrete confined by forms such as for sidewalks, patio sections, and the like.
2. Description of the Related Art:
Applicant's prior U.S. Pat. No. 4,386,901 discloses a concrete screeding apparatus featuring a loose bearing mounted vibrating shaft supported within an elongated open frame. The apparatus of this patent is highly maneuverable in character, and is particularly useful with so-called wet or "mud" type screeding in which forms are not available or used.
Applicant's copending U.S. patent application Ser. No. 888,522, filed July 23, 1986, and entitled, "Portable Screed", the disclosure of which is hereby incorporated by reference, discloses a lightweight, portable vibrating concrete screed composed of a base unit and a selected number of attached extension units. Each unit incorporates an extruded member housing a vibrating shaft within the extrusion and forming a screed surface. A small gasoline engine mounts on a plate forming a part of the base unit extrusion and drives the vibrating shaft. Handles are secured at selected points on selected ones of the extruded members for guiding and propelling the screed.
The aforementioned copending application also discloses various prior art screeds having some form of extrusion as a structural element, including U.S. Pat. Nos. 2,542,979; 2,693,136; 3,095,789; and 4,105,355, the teachings of which are more fully described in said application.
At page 5, lines 15-16 of applicant's copending application Ser. No. 888,522, it is disclosed to connect a base screed unit to screed extension units by means of straps which are secured by bolts. Such mode of connecting the respective adjacent screed units, while simple in construction and readily effected, has the associated disadvantage that the vibrations produced in the extruded units are transmitted to such connections, so that after a period of sustained or intermittent extended use, as a result of the transmitted vibrations, the bolts securing the straps may loosen, so that uncoupling of the connected screed units occurs.
Another disadvantage of the portable screed of the aforementioned copending application is that when a plurality of screed extension units are connected to the base screed unit to provide a screed apparatus of substantial length, there is a tendency, by virtue of the weight of the respective extension units, for the extension units to be deflected from a longitudinal alignment with the base screed unit. This effect may be particularly pronounced in extended length screed assemblies, where progressively increasing "droop" of successively outer extension units produces a marked overall deviation from the desired linear profile.
Accordingly, it is an object of the present invention to provide an improved portable screed of the general type disclosed in the aforementioned copending application, which however is not susceptible in operation to the deficiencies noted above.
It is another object of the present invention to provide a portable, lightweight screed of the aforementioned type, in which adjacent screed units are connected to one another by means which are highly resistant in use to loosening from vibration generated in the screed assembly and transmitted through the structure thereof.
It is yet another object of the invention to provide a portable, lightweight screed of the aforementioned type, which is resistant to the aforementioned progressive "droop" phenomenon, and specifically employs means which allow adjustment of the attitude of adjacent sections relative to one another, whereby predetermined desired surface profiles of the concrete being screeded are readily obtained.
Other objects and advantages of the present invention will be more fully apparent from the ensuing disclosure and appended claims.